Glass can be manufactured into fibers as, e.g., continuous, semi-continuous or blown fibers. Textile fibers may be manufactured by, for example, a direct melt or a marble melt process. The melted glass may be fed to a dedicated bushing typically constructed of a platinum-rhodium alloy. A molten glass stream is passed through an orifice and is cooled to form continuous fibers. Methods of making such fibers may be found in the Engineered Materials Handbook, Vol. 4, Ceramics and Glasses by ASM International (1991), incorporated herein by reference.
Another class of glass fibers is commonly referred to as glass wool or microglass fibers. Microglass fibers may be manufactured, for instance, by well-known manufacturing methods, known as the rotary method and the flame blown method. Another well-known and widely used method is the CAT method, which is a modification of the rotary method. Manufacturing glass by these methods requires heating glass compositions past their melting temperatures into a working temperature range. Typical glass compositions used in making glass fibers have melting temperatures of about 1260 to 1500° C. and working temperatures (temperature ranges between glass viscosity 100 and 10000 poise) of about 920 to 1500° C. Existing compositions have relatively narrow working ranges, making the forming of glass fibers of desirable diameters and lengths difficult because it is difficult to maintain the glass compositions in the workable range. Additionally, the relatively high melting temperatures require large amounts of energy to melt the compositions, which can be very costly.
In addition, typical glass compositions used for making glass fibers have liquidus temperatures 800 to 1000° C. The liquidus temperature of typical compositions used for making glass fibers limits the useful life of fiberization equipment due to the high temperatures at which the equipment must operate. This is especially true when a spinner disc is employed in the fiberization equipment. A glass composition having a relatively low liquidus temperature also is useful for reducing or preventing crystallization of the glass during the fiberization process.
Glass fibers are used in a variety of applications. For such applications glass fibers may be formed into a mat structure. A glass fiber mat is a nonwoven, woven, paper, or textile, made of glass fibers bonded or interlocked together by mechanical, chemical, thermal, or solvent means. Glass fiber mats may comprise only glass fibers or may include other materials as suitable to meet the application specifications.
For example, glass fibers are used in several manners in batteries. Glass fibers are typically used as a separator that is preferably inserted between negative and positive plates of the battery. In addition, glass fibers are used as one of the materials for the active material paste used for the negative or positive plates of a battery. The chemically reactive material (or active material paste) is positioned at the positive or negative electrode to engage in the charge and discharge reactions. Further, glass fibers may be used as a pasting paper that is applied to the surface of the plates to reduce the liberation of lead dust during manufacture and/or to keep plates from sticking together during the curing process.
Glass fibers tend to become brittle in humid environments, leach favorable and unfavorable components, and are unstable in acidic and/or alkaline environments. These characteristics of certain glass fibers can limit their usefulness in applications such as battery separators or filters. Ion leaching, for example, is a glass fiber surface phenomenon based on the glass composition. The amount of ions lost from a glass fiber is proportional to the exposed surface area and the glass composition. Surface area considerations are typically greatest for glass fibers having diameters of less than about 5–7 μm. In some glass fibers certain metal oxide impurities (e.g., platinum oxide, iron oxide) leach out of the fibers and have a detrimental effect on the life of the battery.